Magnetic amplifier circuits



March 22, 1966 R NELSON 3,242,421

MAGNETIC AMPLIFIER CIRCUITS Original Filed May 25, 1960 5 Sheets-Sheet 1Wuhg INVENTOR. Robe/l 5. Nelson "(LEW His A/fome y March 22, 1966 R. E.NELSON 3,242,421

MAGNETIC AMPLIFIER CIRCUITS Original Filed May 23, 1960 5 Sheets-Sheet 3-ll6 l20 I44 2. ,l4? 148 i 350i} l {I 348 g {has 349 L35| 35? 1 I? E i33| I l l 3s2 a o 359 j I l I45 INVENTOR.

283 268 Robert E. Nelson BY a- @RW His A flame y March 22, 1966 R. E.NELSON 3,242,421

MAGNETIC AMPLIFIER CIRCUITS Original Filed May 23, 1960 5 Sheets-Sheet 5I45 473 INVENTOR. 26a 7 Robert 5 Nelson F 1g. 20 BY GEM His AttorneyUnited States Patent Original application May 23, 1960, Ser. No. 30,979,now

Patent No. 3,124,932, dated Mar. 17, 1964. Divided and this applicationMay 22, 1963, Ser. No. 282,321

5 Claims. (Cl. 323-89) This application is a division of my co-pendingapplication Serial No. 30,979, filed May 23, 1960, now United StatesPatent 3,124,932,

This invention relates to magnetic amplifiers and more particularly tomagnetic amplifiers that are useful in controlling the amount of fuelsupplied to a gas turbine or the like in'accordance with turbine inlettemperature.

One of the objects of this invention is to provide a fuel controlamplifier for controlling fuel supplied to a turbo prop engine or thelike in accordance with turbine inlet temperature, that is rugged inoperation, and which requires less field servicing time than thoseheretofore known and which also is accurate in response. This object iscarried forward by employing a series of magnetic amplifiers andassociated circuits which perform the fuel control function.

Another object of this invention is to provide a magnetic amplifier thatis capable of amplifying microvolt inputs and which is self-biasing.

A further object of this invention is to provide a magnetic amplifierarrangement that includes a pair of magnetic amplifiers which areconnected to have their output currents combined through a resistor toform a bias voltage. It has been found that this circuit arrangementprovides little change in output current over large changes in inputline voltages.

Still another object of this invention is to provide a power supply thatis capable of maintaining a constant direct current output, the supplyincluding a magnetic amplifier having a control winding that isenergized from a circuit that includes a Zener diode, the circuit beingenergized from the output of the magnetic amplifier, and further whereinthe magnetic amplifier is self-biasing.

A further object of this invention is to provide a fuel controlamplifier including an overtemperature relay for releasing a temperaturedatum brake, and wherein the circuit for operating the relay includes amagnetic amplifier circuit that causes positive closing and opening ofthe relay contacts.

Another object of this invention is to provide a circuit for operating arelay that includes a magnetic amplifier having a positive feedbackwinding and a negative feedback winding connected with a voltageresponsive circuit element such as a Zener diode. In this circuit smallenergization of the control winding of the magnetic amplifier causes anavalanche energization of the relay coil because of the presence of thepositive feedback winding, this avalanche energization being tempered bythe breaking down of the Zener diode which causes the energization ofthe negative feedback winding.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

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In the drawings:

FIGURE 1 is a block diagram of a fuel control amplifier for controllingthe fuel supplied to a turbo prop engine.

FIGURES 2A, 2B, 2C and 2D taken together are a schematic electricalcircuit diagram of a fuel control amplifier made in accordance with thisinvention.

Referring now to the drawings and more particularly to FIGURE 1, thereference numeral 10 designates a turbo prop engine which drives thepropeller 12. The turbo prop engine 10 is fed with fuel via a pipe 14which is connected with a by-pass pipe 16 and a fuel inlet pipe 18. Thefuel inlet pipe 18 is connected with a main control 20 which is variedby a lever 22 operated by the pilot of the aircraft. It can be seen thatthe main control 20 is connected with a pump 24 having an inletconnected with a source of fuel 26. The inlet is also connected with abypass pipe 28 and it is seen that this by-pass pipe 28 is connectedwith the chamber 30 of a fluid by-pass control valve generallydesignated by reference numeral 32. The by-pass valve 32 has a wall 34formed with an opening 36 that connects the chambers 30 and 38. Ashiftable valve member 40 controls the flow capacity of the opening 36which controls the connection of chambers 30 and 38 The valve 40 isnormally biased to a slightly open position by springs 42 and 44 whichhold the valve in a null position. The valve 40 is shifted by a gear 46having a mechanical connection with a motor designated by referencenumeral 48.

The motor 48 is a two-phase motor and drives a generator 50 having anoutput winding 52. The motor 48 and generator 50 are mechanicallyconnected and are connected with a brake disk 54 which may be contactedby a brake member 56 under the control of a relay coil 58-. When therelay coil 58 is energized the brake is released and under otherconditions the braking member 56 engages the brake disk 54 to hold thevalve 40in a predetermined position.

It can be seen that the fluid circuit that includes pipe 16, chamber 38,orifice 36, chamber 30 and pipe 28 constitute a by-pass for fuel. Thus,the position of valve 40 will control the amount of fuel that isby-passed away from the engine and as will become more readily apparenthereinafter the positioning of this valve is controlled in accordancewith turbine air inlet temperature.

The circuit for controlling the positioning of valve 40 in accordancewith turbine air inlet temperature includes a thermocouple 60 which isconnected with a voltage dividing network 62 and with the junction 64.The voltage dividing network 62 is connected with a constant voltagesource 66 and is also connected with the junction 64. The junction 64feeds a microvolt magnetic amplifier 63 and it is seen that thisamplifier feeds a low level magnetic amplifier 72 and the output of thismagnetic amplifier is fed to a saturable reactor motor drive circuit 74that is connected with the input winding 76 of the twophase motor 48. Arate feedback circuit is provided which includes a phase responsivecircuit 78 that is connected with the output winding 52 of generator 50and which has an output connected with the junction 64. The circuitillustrated in FIGURE 1 also includes a null circuit 80 which isconnected to control the temperature datum brake relay coil 58 and whichis connected with the junction 82.

In the operation of the system illustrated in FIGURE 1, the thermocoupledevelops a voltage in accordance with turbine inlet temperature and thisvoltage is compared with a voltage developed by the potentiometernetwork 62 that is preset to give the desired fuel by-pass for a giventurbine inlet temperature. When the turbine inlet temperature deviatesfrom a desired value, as set up by the potentiometer network 62, anerror voltage is fed to the input of the magnetic amplifier 68 andthrough the amplifiers 70 and 72 to the saturable reactor motor drive74. This causes the motor 48 to operate which, in turn, drives the valve40 in the proper direction to by-pass more or less fuel. When the motor48 operates, it rotates the rotor of generator 50 to produce an outputvoltage in winding 52 that is fed to the phase sensitive circuit 78. Thecircuit 78 has an output which is fed back to the junction 64 so that avoltage is fed to the amplifier 68 which is an indication of the rate ofchange of movement of the valve 40.

Under normal conditions when the fuel control amplifier is operating therelay coil 58 is energized so that the brake 56 does not impede movementof the motor shaft 48 to vary the setting of valve 40 in accordance withturbine inlet temperature. Under certain conditions of operation,however, such as when landing the aircraft, it is desirable to fix thesetting of the valve 40 for a predetermined by-pass of fuel. In such acase suitable circuitry causes the coil 58 to be energized to apply thebrake and fix the valve 40 at its setting at that time. The null circuit80 shown schematically in FIGURE 1, operates to energize the coil 58 tocause the brake to be released upon a predetermined overte'rnperaturecondition which is indicated by a voltage appearing at junction 82 andapplied to the null circuit 80. This null circuit is more fullydescribed hereinafter.

In FIGURE 1, the fuel control system for the turbo prop engine has beenover simplified in order to provide a clear and understandabledisclosure of this system. Thus, the system may be more elaborate thanthat shown in FIGURE 1 and may include elements in addition to the valve32 which are shown in copending application S.N. 464,094 filed on March23, 1955, now Patent 2,938,- 340. This system is also illustrated inBritish Patent 808,920. It can be seen from an inspection of Patent 2,938,340 and the British patent that the fuel control sys tem may includeother elements, for example, a diaphragm operated by-pass valve which isconnected with a Venturi.

FIGURES 2A through 2D which are now to be described, are a schematicrepresentation of the fuel control amplifying circuit of this invention,it being understood that the various figures only form portions of thetotal circuit and that these figures are connected together by leadwires in a manner to be more fully described hereinafter.

Referring now to FIGURE 2B, the reference numeral 84 generallydesignates a transformer having a primary winding 86 connected with thelead Wires 88, 90, 92 and 94. A condenser 96 is connected with the leadwire 92 and in a like manner a condenser 98 is connected with the leadwire '94. The lead wires 88 and 90 form input leads for the transformerand are preferably energized with 115 volt, 400 cycle AC. voltage. It isseen that the lead wire 88 is connected with a lead wire 100 which isconnected with the other portions of the circuit as will be apparentfrom the other figures of the drawing. The transformer, in addition tothe primary winding 86, has center tapped secondary windings 102, 104,106, 108, 110, 112, and 114. The secondary winding 102 is connected withlead wires 116 and 118. The center tap of secondary winding 102 isconnectedwith the center tap of secondary winding 104 and these centertaps are connected to a common lead wire 120. The secondary winding 104has its outer ends connected with lead wires 122 and 124. .Ina similarfashion secondary winding 106 is connected with lead wires 126, 128 and130 whereas secondary winding 108 is connected with lead wires lead wire181.

4 132, 133 and 134. In a like manner, secondary winding is connectedwith lead wires 135, 136 and 137. Secondary winding 112 is connectedwith lead wires 138, 139 and 140. The secondary winding 114 is connectedwith lead wires 141, 142 and 143.

The secondary winding 144 has no center tap and it is connected withlead wires 145 and 146. The secondary winding 147 likewise has no centertap and is connected with lead wires 148 and 150. The same referencenumerals have been used to indicate these lead wires in each of theFIGURES 2A through 2D so that the entire circuit may be readily traced.

As examples of voltages that are obtained from the secondary windingsthe secondary winding 102 may have 36 volts A.C. from center tap toouter conductor, whereas the secondary winding 104 may have 8.9 voltsbetween center tap and outer conductors. The secondary 106 may have 21.5volts between center tap and outer conductors whereas the secondarywinding 108 has 5.4 volts between center tap and outer conductor. Thesecondary winding 110 has 9 volts between center tap and outerconductors and the secondary winding 112 has 27.5 volts between centertap and outer conductors. The secondary winding 114 has 24.6 voltsbetween center tap and outer conductors and the secondary Winding 144has 10 volts across its conductors. The secondary winding 147 has 120volts between its outer conductors.

Referring now to FIGURE 2A, it is seen that the constant voltage sourceis enclosed in dotted lines and is designated by reference numeral 66 asit was in FIGURE 1. AC. input power is fed to this reference voltagesource via the lead wires 126, 128 and 130, which are connected with thesecondary winding 106 of transformer 84. The lead wire 126 is connectedto one side of a load winding 152 of a magnetic amplifier. The oppositeside of load winding 152 is connected with lead wire 154 through arectifier 156. The magnetic amplifier has another load winding 158connected between the lead wire 128 and a rectifier 159. The magneticamplifier includes a negative feedback winding 160, a bias winding 162,and a control winding 163. The negative feedback winding 160 isconnected between lead wire 154 and a junction 164 whereas the biaswinding 162 is connected between a lead wire 166 and the junction 167.It is seen that the control winding 163 is connected between junction168 and the lead wire 169. A voltage responsive diode of the Zener type170 is connected between the junction 168 and the lead wire 166. Theseries connected resistors 171, 172 and 173 are connected between thelead wire 166 and the junction 168. A resistor 174 is connected betweenlead wire 166 and the junction 167. A resistor 175 is connected betweenthe junction 167 and the junction 176. An inductor 17 7 connects thejunctions 164 and 176 and it is seen that condensers 178 and 179 areconnected with opposite sides of the inductor and with the lead wire166. The junction 176 is connected with a junction 180 and it is seenthat both of these junctions are connected with a The lead wire 166 isconnected with lead wire 138 at junction 182 and is also connected withlead wire 183 at this junction.

The circuit designated by reference numeral 66 and which has just beendescribed operates to provide a constant 10 volts across the lead wires181 and 183 even though the AC voltage input from leads 126, 128 and 130may vary. When AC. power is supplied to the circuit 66 there is no biascurrent and the output voltage rapidly builds up until the output isapproximately 10 volts between junction 180 and lead wire 166. Theresistors 172 and 173 are so chosen that their sum is equal toapproximately 1000 ohms and the voltage across resistor 173 is the sameas the voltage across the Zener diode 170 when separate 10 milliampsflows through the diode. If the voltage output should tend to be greaterthan 10 volts a voltage greater than the Zener voltage would appearacross the resistor 173 and control current will '5 flow through thecontrol Winding 163 in such a direction as to make the output return tovolts. In other words, when the output voltage changes across junction180 and lead wire 166 the difference in potential of junctions 168 and184 also changes to cause a change in the control current flowingthrough control winding 163 and, thus, change the saturation of themagnetic amplifier to reduce or increase the voltage applied to thejunction 180 and lead wire 166.

It will be appreciated that the inductor 177 and the condensers 178 and179 form a filter circuit for the power supply 66. It is also to bepointed out that the voltage reference circuit 66 is self-biased byutilizing the voltage output fed back in a negative direction throughthe bias setting resistor 175. The effect of this type of biasing istwofold; first performing the biasing action and secondly acting as aminor loop in voltage regulation. This is accomplished since, should thevoltage tend to decrease, the bias current would also decrease changingthe bias point in the direction to increase the output of the magneticamplifier.

It can be seen from FIGURE 2A that the voltage output from the voltagereference source 66 appears across lines 181 and 183 and it is seen thatthese lines are connected with the voltage dividing or potentiometernetwork 62. As is clearly apparent from FIGURE 2A this resistor network62 includes the resistors 190 and 192 which are connected directlyacross the output of the voltage reference circuit 66. Also connecteddirectly across this output is a network including the resistors 193,194 and 195. Another network including resistors 196, 197 and 198, isconnected across the voltage output of thereference circuit 66. Thejunction 199 is connected to a lead wire 200. This lead wire 200' andthe lead wire 201 are connected with the thermocouple 60 and thus formthe thermocouple input for the fuel control amplifier.

The junctions 203 and 204 are connected together by a potentiometer 205having a slider 206 connected with the lead wire 207. The lead Wire 207is connected to a fixed contact 208 of a relay having a shiftablecontactor 209 operated by the relay coil 210 and having another fixedcontactor 211. When the relay coil 210 is de-energized the shiftablecontactor 209 engages the fixed contact 211. When the coil 210 isenergized the contactor 209 is shifted over into engagement with thefixed contact 208. The fixed contact 211 is connected with a lead wire212 which is, in turn, connected to the slider 213 on a potentiometer214. It can be seen that the potentiometer 214 is connected across theresistor 197.

The lead wire 181 is connected with a'resistor 215 and it 1s seen thatthis resistor is connected with junction 216. The lead wire 183 isconnected with resistor 217 and this resistor is connected with junction218. Connected across the junctions 216 and 218 are the resistors 219and 220. .The lead wires 221 and 222 are connected across the resistor219. These lead wires 221 and 222 are connected with a coordinatorgenerally designated by reference numeral 223 which is illustrated inFIGURE 2B. This coordinator includes a potentiometer 224 having a slider225 connected with a lead wire 226. The slider 225 may be operated bythe pilot control lever.

The junction 216 is connected with lead wire 227 through a resistor 228.The junction 218 is connected with potentiometer 229 having a slidabletap 230a. The lead wire 227 is connected with potentiometer 230 having aslider 231. It is seen from FIGURE 2A that the lead wire 222 isconnected with the junction 232.

The relay coil 210 has one side thereof connected with lead wire 233 andhas an opposite side thereof connected with junction 234. The junction234 is connected with lead wires 235 and 236. The lead wire 233 isconnected with a relay box of the system which is not illustrated andthe lead wire 235 is connected with one side of a 24 Volt direct currentpower source.

The shiftable contactor 209 is connected with a lead wire 237 which isconnected with the fixed contact 238 of another relay illustrated inFIGURE 2B. It is seen that this relay includes a coil winding 239 thatoperates the shiftable contactor 240. This relay further includes afixed contact 241 connected with lead wire 226 and when the coil 239 isde-energized the contactor 240 will engage the contact 241. When therelay coil 239 is energized the contactor 240 is shifted into engagementwith the fixed contact 238. It is seen that one side of the relay coil239 is connected with the lead wire 236 which is one side of the 24 voltdirect current power source. The lead wire 236 is connected withjunction 242 and this junction is connected with a lead wire 243. Thelead wide 243 extends into the circuit illustrated in FIGURE 2C and isconnected with a terminal block having a junction point 244. Thisjunction point is connected with the temperature datum valve brake 58.The lead 243 is also connected with a junction 245 that is in turnconnected to a relay coil 246. The opposite side of relay coil 246 isconnected with lead wire 247 and the junction 248. The junction 248 isconnected with a point 249 on the terminal board that is connected witha relay box (not shown). It is seen that the opposite side of the relaycoil 246 is also connected with junction 250 that is connected with thelead wire 251. The relay coil 246 operates the shiftable contactors 252and 255 which are respectively in engagement with fixed contacts 254 and253 when the relay coil is de-energized. When the relay coil 246 isenergized the shiftable contactors are shifted into engagementrespectively with fixed contacts 256 and 257. It is seen that the leadwire 251 is also connected to one side of the relay coil 239 illustratedin FIGURE The relay coil 210 is a speed sensitive slave relay whereasthe coil 239 is a limit select relay. The relay 246 and its associatedcircuits are also a limit select relay.

Referring now once more to FIGURE 2A, it is seen that the lead wide 201which is connected to one side of the thermocouple is connected with ajunction 260'. This junction 260 is connected with lead wire 261 and isalso connected with the resistor 262. The opposite side of resistor 262is connected with junction 263 which, in turn, is connected withjunction 264 and the lead wire 145. The junction 263 is also connectedwith resistor 265, the opposite side of this resistor being connectedwith junction 266. The junction 266 is connected with lead wires 267 and268. The lead wire 267 is connected with the shiftable relay contactor240 as is clearly apparent from FIGURE 2B. The junction 264 is connectedwith a lead wide 269.

The voltage outputs of the thermocouple 60 and the potentiometer network62 are algebraically added and the resultant error voltage is applied tothe magnetic amplifier circuit 68 via the lead wires 261 and 269. Thelead wire 261 is connected with the control winding 270 of one of thetwo magnetic amplifiers that make up the total magnetic amplifiercircuit 68. The left hand magnetic amplifier includes this controlwinding 2.70, a bias winding 271, a feedback winding 272 and a'pzair ofload or gate windings 274 and 276. The load windings 274 and 276 areboth connected with a comm-on lead 270 that is connected betweenresistors 279 and 280. 7 It is seen that the resistor 280 is connectedwith one side of the feedback winding 272. This feedback winding has itsopposite side connected with junction 281 and this junction is connected with resistor 282 and a lead wire 283. The load windings 274 and276 are connected with rectifiers 284 and 285, the rectifier 285 beingconnected with a junction 286 and the rectifier 284 being connected withjunction 287. The junction 286 is connected with rectifier 288 whereasthe junction 287 is connected with rectifier 289. The junction 286 isalso connected with a lead Wire 132 and the junction 287 is connectedwith a lead wire 134. The lead wires 132, 133 and 134 form the input.power terminals to the magnetic amplifier circuit 68 and and a biaswinding 298. One side of the feedback winding 294 is connected withresistor 300, the opposite side of this winding being connected withjunction 301. The junction 301 is connected with resistors 302 and 303and is also connected with the lead wire 304. The resistors 282 and 303are connected with a junction 305 via the resistors 306 and 307. Thejunction 305 is connected with junction 308 and this junction isconnected to a resistor 309 and to a lead wire 310. The lead wire 310 isconnected to one side of bias winding 271 and, thus, to one side ofresistor 311. The opposite side of resistor 311 is connected with a leadwire 312 and this lead wire is connected to one side of a bias winding298 and the resistor 313.

As noted hereinbcfore the A.C. power to the magnetic amplifier circuit68 is coupled thereto via the lead wires 132, 133 and 134, and directcurrent power is taken off the magnetic amplifier circuit via lead wires304 and 283 which are connected with the junctions 281 and 301. It willbe appreciated that in this circuit the saturation of the two magneticamplifiers is controlled by the feedback, bias and control windings sothat the two amplifiers have their firing point varied in accordancewith the current flow to the various winds. The rectifiers 285, 288, 284and 289 provide direct current output from the magnetic amplifiercircuit 68.

The magnetic amplifier circuit 68 is self-biasing and, thus, requires noexternal biasing supply. The circuit is designed such that with a givenfiring angle in both of the magnetic amplifiers, the current throughresistors 282 and 306 is equal to the current through resistors 303 and307 and is equal to approximately 2 /2 milliamps. It can be seen thatthese currents combine through the resistor 309 to form a bias voltage.This voltage causes a biasing current to flow through the bias windings271 and 298 and is trimmed by resistors 311 and 313 to allow for thetolerances in winding resistances and core variations. The action ofthis biasing circuit under conditions of varying line voltage is veryimportant.

As line voltage is varied upward the voltage out of the magneticamplifiers tends also to increase upward thereby increasing the voltageacross resistor 309. This, in turn, furnishes more biasing current whichchanges the firing angle to a new voltage output. The net effect of thisis very small changes in the output current over large changes in theline voltages. Other advantages of this system of biasing are that thetotal sum of the current flowing through resistors 279 and 306 andthrough resistors 303 and 307 are maintained as a constant over theoperating range of the two magnetic amplifiers. Thus, if the currentthrough resistors 279 and 306 increases by one milliamp, for example,the current flow through resistors 303 and 307 must decrease by onemilliamp and the two magnetic amplifiers can be prevented from flipfiopoperation and both are held in their operating ranges.

The amplifier 68 may be thought of as a voltage amplifier rather than asa current amplifier with a gain fixed by the bridge resistors 279, 306and 303 and 307. It will, of course, be appreciated that the voltageinput to the magnetic amplifier 68 is in the microvolt range and thatthis voltage input will control the firing angles of the magneticamplifiers to provide a direct current output across lead wires 283 and304 which is applied to the low level amplifier generally designated byreference numeral 70 and shown in detail in FIGURE 2B.

Referring now more particularly to FIGURE 2B, it is seen that the leadwires 283 and 304 coming from the magnetic amplifier circuit 68 are fedto the magnetic amplifier circuit 70. The magnetic amplifier circuit 70includes a first magnetic amplifier having load windings 320 and 322.This amplifier also includes a bias winding 324, a control winding 326and a feedback winding 328. The bias winding 324 is shunted by aresistor 329 and the bias winding and resistor are connected betweenlead wires 330 and 331. The control winding 326 has its one sideconnected with lead wire 304 and has its opposite side connected withlead wire 332. The feedback winding 328 is connected with junction 333and it is seen that this junction is connected with resistors 334 and335 and with a conductor 336 connected with junction 337. The junction337 is connected with a junction 338 which is, in turn, connected withthe lead wire rectifiers 340 and 341, one side of these rectifiers beingconnected with lead wires 137 and 135.

The other magnetic amplifier includes load windings 345, and 346, afeedback winding 347, a control winding 348 and a bias winding 349shunted by the resistor 350. One side of the bias winding 349 and theresistor 350 are connected with lead wire 136 and resistor 351. Theresistors 351 and 335 are connected by a lead wire 352. The load winding345 and one side of the feedback winding 347 are connected by a resistor342 and in a like manner, one side of the load winding 320 and thefeedback winding 328 are connected by a resistor 353. One side of thefeedback winding 347 is connected with a junction 354 and this junctionis connected with resistors 355, 356, 357 and the lead wire 358. Thejunction 337 is connected with junction 359 via a resistor 360 and it isseen that the junction is connected to one side of resistor 357. Aresistor 361 is connected between resistor 356 and the lead wire 330.The junction 359 is connected to one side of the control winding 348 viaa lead wire 362.

AC. input power is supplied to the magnetic amplifier circuit 70 fromthe transformer secondary 10 via the lead wires 135, 136, and 137. Thesignal input to the magnetic amplifier 70 comes through the lead wires283 and 304 from the magnetic amplifier circuit 68. This low levelamplifier 70 is generally similar to the microvolt amplifier 68 exceptthat a higher operating voltage is placed on the load winding and theoutput range is six times higher. The manner of obtaining feedback isalso somewhat different.

The output power from the magnetic amplifier circuit 70 is taken fromjunctions 333 and 354 and is passed on to the magnetic amplifier circuit72 via the lead wires 358 and 283. The magnetic amplifier 72 shown inFIG- URE 2C is similar to the magnetic amplifiers 68 and 70 and includesa pair of amplifiers, one of which has the load windings 363 and 364, acontrol winding 365 and a bias winding 366 shunted by a resistor 367.The other amplifier includes the load windings 368 and 371, a controlwinding 369 and a bias winding 370 shunted by the resistor 372.

T he bias windings shunted by their resistors are connected by a leadwire 374 and the control windings are connected by a lead wire 375. Thebias windings 366 and 370 are connected by a circuit that includes theresistors 380 and 381 plus the conductor 382. The load windings 363 and364 are connected with a lead wire 383 which is connected with junctions384 and 385. The junction 385 is connected with junction 386 via aresistor 392 and the junction 384 is connected with a resistor 388. Theopposite side of resistor 388 is connected with a lead Wire 387 whereasthe junction 386 is connected with resistors 392, 389 and 390. A leadwire 391 connects lead wire 382 with the junction 394. The junction 393is connected to one side of the load windings 368 and 371 via the leadwire 398 and is also connected with a lead wire 395. One side of thecontrol winding 369 is connected with a lead wire 396. The junction 386is corr- .tions 386 and 393 and 9 nected with a lead wire 397 as isclearly apparent from FIGURE 20.

The load windings 363 and 364 are connected with rectifier-s 400 and 401whereas the load windings 368 and 371 are connected with rect-ifiers 402and 403. The rectifiers 400 and 402 are fed from the line 140 whereasthe rectifiers 401 and 403 are fed from the line 138. The AC. powerinput for the magnetic amplifier circuit 72 comes from the secondarywinding 112 via the lead wires 138, 139 and 140. As noted hereinbeforethe direct current signal from magnetic amplifier circuit 70 is appliedto the magnetic amplifier circuit 72 via the lead wires 358 and 283. Themagnetic amplifier circuit 72 operates to amplify this direct currentvoltage by varying the saturation of the two magnetic amplifiers of thiscircuit in accordance with the signal voltage which it receives from themagnetic amplifier circuit 70. The output voltage of magnetic amplifiercircuit 72 is developed across the juncis, thus, applied to the leadwires 395 and 397.

The output voltage appearing across leads 395 and 397 is used to drive asaturable reactor stage which is generally designated by referencenumeral 74 and which is enclosed in dotted lines in FIGURE 2D. Thissaturable reactor motor drive circuit includes the load windings 420,422, 424 and 426, which are connected together as shown. The lead wires148 and 150 which are energized from secondary winding 147 of thetransformer 84 are connected with the load windings in a manner which isclearly apparent from FIGURE 2D. The saturable reactor motor drive alsoincludes the bias windings 428 'and 429. One side of the bias winding429 is connected with a lead wire 430 which, in turn, is connected toone side of a potentiometer 431 having a slider 432. The slider 432 isconnected with a resistor 434, the opposite side of this resistor beingconnected with a junction 435. The junction 435 is connected withrectifiers 436 and 437 which are connected with lead wires 141 and 143.The lead Wires 141 and 143 are connected with the secondary winding1140f transformer 84.

The bias winding 429 is connected with a junction 450 and it is seenthat this junction is connected with lead wire 451 which connects withone side of the potentiometer resistor 434 through lead wire 452 andcontrol winding 428. The junction 450 is connected with the lead wire142 which is the center tap of the secondary winding 114.

which is, in turn, connected with junction 464 and the lead wire 396.The junction 464 is connected to one side of a resistor 465, theopposite side of this resistor being connected with lead wire 466. Oneside of the control winding 461 is connected with a lead wire 470 as isclearly apparent from an inspection of FIGURE 2D. The output of thesaturable reactor circuit 74 is taken off at junctions 471 and 472 whichare connected respectively with lead wires 473 and 474, It is seen thatthe lead wire 473 is connected with the line 100 and that the lead wires474 and 473 are brought out to a junction block 475. The lead wire 474is connected with the twophase motor 48 whereas the lead wire 473 formsa 115 volt common lead.

Referring now more particularly to FIGURE 2C the null circuit 80 whichis enclosed in dotted lines will now be described. The null circuit 80is designed to control the energiza-tion of a relay that includes therelay coil 500, the shiftable contactor 501 and the fixed contact 502.When the relay coil 500 is de-energized the contactor 501 remainsout ofcontact with the fixed contact 502 but when the relay coil 500 isenergized the shiftable contactor 501 is shifted into engagement withthefixed contact 502. The fixed contact 502 is connected with a leadwire 503 that leads to a point 504 on a junction block. The point 10 504of the junction block is operative to control the brake relay 58illustrated in FIGURE 1. The circuit designated by reference numeraloperated to cause positive operation of the relay which includes thecoil 500 in a manner to be more fully described.

It can be seen that the null or relay operating circuit 80 includes amagnetic amplifier having load windings or gate windings 505 and 506both of which are connected to a common lead wire 507. The load winding505 is connected with a rectifier 508 whereas the load winding 506 isconnected with the rectifier 509. The opposite side of rectifier 508 isconnected with lead wire 116. The opposite side of rectifier 509 isconnected with lead wire 118 which is connected to the transformerwinding 102.

The magnetic amplifier of relay operating circuit 80 in addition to theload winding includes a positive feedback winding 510, a negativefeedback winding 511, a control winding 512 and a bias winding 513. Thebias winding 513 has one side thereof connected with lead wire 120 andhas an opposite side connected with the junction 514. A resistor 515 isconnected between lead wire 120 and the junction 514 and a resistor 516is connected between junction 514 and 517. A resistor 518 connects thejunctions 519 and 517 and a rectifier 520 is connected between thejunction 519 and the lead wire 122. A rectifier 521 is connected betweenjunction 519 and the lead wire 124. A series connected resistor 522 andrectifier 523 are connected between junction 517 and the lead wire 120.A condenser 524 connects the junction 519 with the lead wire 120 and itis seen that the lead wire 120 is connected with the lead wire 525. Thelead wire 525 is connected with junction 526 as is clearly apparent fromthe drawing. The control winding 512 of the magnetic amplifier circuitis connected to the lead wires 397 and 530. The lead wire 530 isconnected to one side of a resistor 531, the opposite side of thisresistor being connected with lead Wire 532. Lead wire 532 is connectedwith the shiftable contactor 252 and is connected with the junction 533.A rectifier 534 connects the junction 533 and the fixed contact 254. Theopposite side of rectifier 534 is connected with the lead wire 470 as isclearly apparent from an inspection of FIGURE 2C.

The negative feedback winding 511 has one side thereof connected withlead wire 525 and has an opposite side connected with a Zener diode 536.The Zener diode 536 one side of resistor 541 and to one side of thepositive feedback winding 510. A condenser 542 is connected be tweenlead wire 540 and the junction 526. One side of the relay coil 500 isconnected with the lead wire 544 and it is seen that this lead wire isconnected with the shiftable contactor 255 that is operated by relaycoil 246.

The positive feedback winding 510 is connected with lead wire 507 via aresistor 550 and is connected with a junction 551. Thelead wire 243shown in the top portion of FIGURE 2C, as has been noted hereinbefore,is connected with the point 244 of a junction block. This junction blockhas another junction point 552 which is connected with junction point553 on the other junction block. The junction point 553 is connectedwith an electric-a1 datum control switch whereas the junction point 552'is connected with a circuit that controls the temperature datum valvebrake.

The null circuit designated by reference numeral 80 which has now beendescribed, is fed with AC. power from the lead Wires 116, 118 and 120which are connected with the secondary winding 102. The bias winding 513is fed from the lead wires 122 and 124 and, thus, from the secondary 104of transformer 84. The control winding 512 is fed from the junctions 386and 393 of FIG- 'URE 2C which are output terminals of the magneticamplifier circuit 72. It can be seen that the junctions 386 and 393 alsoserve to drive the saturable reactor motor drive circuit '74.

When the null circuit 80 is energized bias current through the biaswinding 513 is adjusted by the resistor 515 to cut off the output of themagnetic amplifier at all times. In other words, with a zero or negativecontrol current the output is very small and is below the voltagenecessary to drive the relay coil 500. The relay coil therefore remainsde-energized and the shiftable contactor 501 does not become engagedwith the contact 502. When a positive control current, however, iscaused to flow in the control winding 512 this current flow subtractsfrom the biasing due to the bias winding 512 and the magnetic amplifierwill have a small output which begins to flow through the relay coil 500via the lead wire 540. Part of this current flows through the positivefeedback winding 510 which further reduces the biasing of the magneticamplifier. The net effect of the positive feedback is an avalancheeffect which causes the amplifier, once started, to saturate and placefull output across the relay coil 500. After the voltage reaches apreset level, however, the Zener diode 536 will fire causing current toflow through the negative feedback winding 511 and this action holds thevoltage across the relay coil 500 at the level desired and keeps theamplifier from fully saturating and thus maintaining it in its operatingrange. If it were not for the Zener diode and negative feedback windingcircuit it is possible that the relay coil 500 would not becomede-energized when the control current reverses or becomes zero. With thesystem described when the control current does become zero or reverses,the relay coil 500 will not be energized sufficiently to maintain thecontactor 501 in engagement with the contact 502. It thus is seen thatthe negative feedback winding and Zener diode play an important part inthe functioning of the null circuit 80.

The null circuit 80 will be energized when the voltage at the outputjunctions 393 and 386 of magnetic amplifier 72 is of such a value as toindicate a dangerous overtemperature condition of the engine. Thus, inthe limiting mode of operation and during landing the pilot may actuatesuitable circuits which will cause the brake 56 to engage the brake disk54 to hold the fuel control in a predetermined position. The function ofrelay coil 500 is to cause an energization of the relay coil 58 wherethe temperature increases to such a point that it is imperative thatthebrake be released. The null circuit 80 will thus sense this condition bythe voltage applied to it from the magnetic amplifier 72 and will causethe relay 500 to be energized when required. The null circuit providesfor circuit 78 and this circuit supplies a signal to the input ofmagnetic amplifier 68 that is an indication of the direction of rotationof the rotor of generator 50 as well as its rate of change of speed.

The demodulator or phase responsive circuit 78 includes a pair of pnptransistors 600 and 601 each having emitter, collector, and 'baseelectrodes. It is seen that the emitter electrodes of these transistorsare connected by resistors 602, 603 and the potentiometer 604 having aslider 605. The slider 605' is connected with a junction 606 and thisjunction is-connected with junction 607 via lead wire 630. The junction607 is connected between rectifiers 608 and 609, rectifier 609 beingconnected to lead wire 146 and the rectifier 608 being connected withlead wire 268. The base electrodes of transistors 600 and 601 areconnected with resistors 610 and 611. The resistors 612 and 613 areconnected respectively across the emitter and base electrodes of thetransistors 600 and 601. It is seen that the resistors 610 and 611 areconnected with a common lead wire 615 whereas the junction 606 isconnected with lead wire 616. A rectifier 617 is connected directlyacross the lead Wires 615 and 616. The lead wires 615 and 616 extendover into FIGURE 20 and it is seen that these lead wires in FIGURE 20are connected with junction points 620 and 621 on a junction block. Thejunctions 620 and 621 are connected with the output of the tachometergenerator 50, this output winding being designated by reference numeral52 in FIGURE 1.

In the operation of the demodulator or phase responsive circuit 78, andas has been noted hereinbefore, the output of the tachometer generator50 of FIGURE 1 is applied to the lead wires 615 and 616 and this voltageduring a half cycle of the AC. voltage will cause the transistors 600and 601 both to become conductive from collector to emitter at the sametime. On the other half cycle of applied voltage both of the transistors600 and 601 will be rendered nonconductive between collector and emitterbecause of the voltages applied between base and emitter. During thetime that the transistors 601 and 600 are conductive from emitter tocollector current will flow through one of the rectifiers 608 and 609and will also flow through the load resistor 265 illustrated in FIGURE2A. This circuit will be energized from the secondary winding 144 oftransformer 84 via the lead wires 145 and 146.

Assuming that on a first half cycle of applied voltage from thetachometer generator both transistors 600 and 601 are renderedconductive and further assuming that at this time the lead wire 146 ispositive with respect to lead wire 145, a circuit may be traced fromsecondary winding 144, through lead wire 146, through the collec tor andemitter path of transistor 601, through resistor 602, through theshiftable tap 605 to the junction 606, through the lead wire 630,through rectifier 608, through lead wire 268, through the load resistor265, and thence through lead wire 145 back to the opposite side of thetransformer winding 144. It will be observed that the current flowthrough resistor 265 is in one direction and is direct current, due tothe provision of the rectifier 608.

7 It will be appreciated that on the other half cycle of applied voltagefrom the tachometer generator there will be no voltage developed acrossresistor 265 since both transistors 600 and 601 will be nonconductive.

If the phase angle of the output voltage of the tachometer generator isshifted due to a reverse in direction in rotation of the rotor of thetachometer generator a voltage will be developed across resistor 265that is of an opposite polarity. With such an arrangement, current willnow flow from transformer secondary winding 144, through lead Wire 145,through resistor 265, through lead wire 268, through the collector toemitter circuit of transistor 600, through resistor 603, through aportion of the resistor 604 to the tap 605, through junction 606,through lead wire 630, through the rectifier 609, and back through leadwire 146 to an opposite side of the secondary winding 144. With thismode of energization it is seen that the current flow through the loadresistor 265 has been reversed due to a reversal in direction ofrotation of the rotor of tachometer generator 50. This tachometergenerator is sometimes referred to as an eddy current type having aninput winding and an output winding and wherein the output voltage isout of phase with the input voltage.

It can be seen from the foregoing that the circuit 78 develops a voltageacross resistor 265 which is dependent upon the phase relationship ofthe output voltage of the tachometer generator and the output voltage ofsecondary winding 144. This voltage, as can be seen from FIGURE 2A, isfed to the input of the magnetic amplifier 68 as well as the signalvoltage that is developed as a result of the thermocouple input beingcompared with a preset setting of the resistance network 62. It willalso be appreciated that the signal that is fed back to the magneticamplifier 68 is indicative of the direction of rotation of thetachometer generator and also will be an indication of its accelerationsince its output voltage is proportional to its speed and will controlthe conductivity of transistors 600 and 601.

The relay 210 illustrated in FIGURE 2A, as has been noted hereinbefore,is a speed sensitive slave relay which has its energization controlledthrough a relay box in accordance with the speed of the turbo propengine. Thus, under certain speeds of the turbo prop engine the relaywill remain de-energized so that the contactor 209 is in engagement withthe fixed contact 211 and thus completes a circuit to the potentiometer214 which is the normal limit potentiometer. Under other conditions ofoperation, the relay coil 210 will be energized to shift the contactor209 into engagement with fixed contact 208 and bring the potentiometer205 into play which is the start limit potentiometer. As an example ofrotational speed, the speed sensitive slave relay 210 may be energizedwhen the engine is below 94% of its rated speed and will be de-energizedat speeds above this speed.

The limit select relays 239 and 246 are controlled from the relay boxand are connected with the coordinator 223. These relays serve to makeswitching connections in accordance with shifting of the pilot controllever. As an example, the shifting may occur when the pilot controllever is open from less than 63 to a point greater than 63".

In summarizing the operation of the system which now has been described,it is apparent that the voltage developed by the thermocouple 60 in theair inlet of the engine is compared with a voltage developed in theresistor network 62 and that the algebraic addition of these voltages isapplied to the input of the magnetic amplifier 68. The output ofmagnetic amplifier 68 is then fed through magnetic amplifiers 70 and 72to saturable reactor motor drive circuit 74 where it causes the twophase motor 48 to drive the valve 40 and the tachometer generator 50.The tachometer generator feeds the phase sensitive circuit 78 and theoutput of this circuit is fed back to the input of the magneticamplifier 68 to provide a rate feedback. As has been noted hereinbefore,the temperature datum brake will be released by the null circuit 80whenever the output of the magnetic amplifier 72 is such as to cause themagnetic amplifier 80 to sufficiently energize the relay coil 500. Itwill be appreciated from the foregoing that the fuel control amplifiervaries the by-passing of the fuel to the engine 10 in accordance withthe turbine inlet temperature which is sensed by the thermocouple 60.

It is important to note that this fuel control amplifier employs nothermionic tubes and therefore is rugged in operation and accurate inresponse. It is also noted that this amplifying system consists entirelyof magnetic amplifiers which are designed to have an accurate responsebut which yet are rugged enough in operation to meet the requirements ofthis type of system.

While the embodiments of the present invention as herein disclosedconstitute preferred forms, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. A magnetic amplifier circuit comprising, a first magnetic amplifierincluding a first load winding and a first control winding, a secondmagnetic amplifier including a second load winding and a second controlwinding, a source of A.C. voltage, a rectifier means connected with saidload windings and said source of A.C. voltage, a first bias winding forsaid first magnetic amplifier, a second bias winding for said secondmagnetic amplifier, first and second output circuits connectedrespectively with said magnetic amplifiers, a voltage developing circuitelement connected with said output circuits whereby the current flowfrom said output circuits is combined through said voltage developingcircuit element, means connecting the bias windings of said first andsecond magnetic amplifiers with said voltage developing circuit elementand a resistor connected across each bias winding.

2. A magnetic amplifier circuit comprising, a first magnetic amplifierhaving a first bias winding, a first control winding, and a first pairof load windings, a second magnetic amplifier having a second biaswinding, a second control winding and a second pair of load windings, asource of A.C. voltage, rectifier means connected with said source ofA.C. voltage and the load windings of both amplifiers, a first circuitnetwork connected with said first load windings, a second circuitnetwork connected with said second load windings, a resistor connectedwith both of said circuits where-by current produced by both of saidcircuits is combined and passed through said resistor, means forconnecting said resistor with said bias windings, means for applying acontrol potential to said control windings and a resistor connectedacross each bias wind 3. A magnetic amplifier circuit comprising, afirst magnetic amplifier having a first bias winding, a first controlwinding and a first pair of load windings, a second magnetic amplifierincluding a second bias winding, a second control winding and a secondpair of load windings, a source of A.C. voltage including a windinghaving a center tap and a pair of outer lead wires, means connectingsaid outer lead wires with said load windings including a plurality ofrectifiers, a circuit connecting said load windings with said center tapincluding a resistor, means connecting said resistor with said biaswindings whereby the current flow through said bias windings is afunction of the voltage developed across said resistor, means forapplying a control potential to said control windings and a resistorconnected across each bias winding.

4. A magnetic amplifier circuit comprising, a first magnetic amplifierhaving a first bias winding, a first control winding, and a first pairof load windings, a second magnetic amplifier having a second biaswinding, a second control winding and a second pair of load windings, athree terminal A.C. power supply, rectifier means connecting the outerterminals of said power supply with said first and second pairs of loadwindings through a plurality of rectifiers, a first circuit networkconnected with said first load windings including a plurality ofresistors, a second circuit network connected with said second loadwindings including a second plurality of resistors, junction pointsintermediate resistors in said first and second circuit networksdefining output terminals for said magnetic amplifier circuit, aresistor connecting said first and second circuit networks with a thirdterminal of said A.C. power source, means connecting said bias windingswith said resistor whereby said bias windings are energized inaccordance with the voltage developed across said resistor, means forapplying a control potential to said control windings and a resistorconnected across each of said bias windings.

5. A magnetic amplifier circuit comprising, a first magnetic amplifierincluding a first pair of load windings, a first feedback winding, afirst control winding, and a first bias winding, a second magneticamplifier including a second pair of load windings, a sec-ond feedbackwinding, a second control winding and a second bias winding, a source ofA.C. voltage including a secondary winding of a transformer having apair of outer conductors and a center tap conductor, means connectingsaid outer conductors with said first and second pairs of load windingsincluding a plurality of rectifiers, means energizing said first andsecond feedback windings from said rectifiers, means connecting saidfirst and second control windings with a source of control potential,means providing a return current path from said rectifiers to saidcentertap conductor including a resistor, means connecting said resistorwith 1 5 said bias windings whereby the current through said biaswindings is a function of the voltage developed across said resistor anda resistor connected across each of said bias windings.

References Cited by the Examiner UNITED STATES PATENTS 2,552,952 5/1951Gachet et a1. 323--89 2,760,148 8/1956 Sakamoto 32389 16 Rowley 323--89Perkins 32389 Chen 317-148 McFarland 317-148 Ringelman v32389 Lafuze32389 LLOYD MCCOLLUM, Primary Examiner. ROY LAKE, Examiner.

2. A MAGNETIC AMPLIFIER CIRCUIT COMPRISING, A FIRST MAGNETIC AMPLIFIERHAVING A FIRST BIAS WINDING, A FIRST CONTROL WINDING, AND A FIRST PAIROF LOAD WINDINGS, A SECOND MAGNETIC AMPLIFIER HAVING A SECOND BIASWINDING, A SECOND CONTROL WINDING AND A SECOND PAIR OF LOAD WINDINGS, ASOURCE OF A.C. VOLTAGE, RECTIFIER MEANS CONNECTED WITH SAID SOURCE OFA.C. VOLTAGE AND THE LOAD WINDINGS OF BOTH AMPLIFIERS, A FIRST CIRCUITNETWORK CONNECTED WITH SAID FIRST LOAD WINDINGS, A SECOND CIRCUITNETWORK CONNECTED WITH SAID SECOND LOAD WINDINGS, A RESITOR CONNECTEDWITH BOTH